This invention relates to an alarm system which employs a radio frequency transmitter and a frequency compatible receiver that couples into a telephone system to ring a remote telephone and deliver a message into the receiver of the remote telephone. More particularly, this invention relates to an alarm system of the type referred to above which is useable on any subscriber telephone line serviced by Touch Tone.RTM. equipment or for telephone exchanges which have Touch Tone.RTM. equipment intermixed with dial type handsets, such exchanges using what is commonly called cross bar dialing.
Common telephone equipment that has been in use for the past forty years has universally used a circular dial type telephone and dialing sequence in which a digital (conducting or nonconducting) sequence of switch openings are used commensurate with the number in the sequence being dialed. Thus, the number three (3) dialed in the sequence results in three interrupts of the natural-state voltage, which is recorded, stored, and used by the central equipment processing the dialing sequence. While providing reasonable access and speed, it can be seen that the logic thus used results in high dialing times for the larger numbers (i.e., 7, 8, 9) and dialing times which are expensive in the aggregate since they result in the seizure of the central processing equipment until such time as the dialing sequence is completed. The dialing function thus produced is also necessarily a high consumer of electrical energy, as well as being slow and cumbersome, since it is necessary to have sufficient energy levels to activate the relay armatures used in the central processing equipment.
More recently, the introduction of the "Touch Tone.RTM. dialing" has provided a telephone communications systems which yields improved dialing speeds, that is, acquisition of the desired subscriber, reduced dialing errors, and better utilization of central processor equipment. The Touch Tone.RTM. dialing system is now well-known in the art, and consists of a series of unique tone-combinations to activate the dialing sequence. These tones are generated by the subscriber's equipment using an audio oscillator and amplifier to generate eight individual tones, which are then used in combinations to represent one of the ten digits (i,e, numbers one through nine plus zero). These tones are all in the audible range from 697 Hz to 1633 Hz (the latter being a spare function). Each tone is selected for its lack of low-beat harmonics. The tones thus generated are used exclusively for the dialing operation and are used in pairs, so as to make twelve unique combinations of tones. Each combination includes a low tone (697, 770, 852, or 941 Hz) and a high tone (1209, 1336, or 1477 Hz) which complete the dialing sequence without the benefit of the digital (logic 0, logic 1 make or break counting) dialing used in previously commonly distributed equipment.
A subscriber, choosing to call another subscriber whether the latter is Touch Tone.RTM. equipped or not, presses the key switches in sequence, generating at each keying action the proper combination of tones uniquely representing each number (0 through 9) in the decimal system. These combinations of tones are sensed by the system central processing equipment to select the proper exchange and subscriber upon that exchange. No switch interrupts are imposed by the subscriber equipment or required by the telephone company's central processing equipment in order to initiate or complete the dialing sequence. Therefore, in lieu of counting dial interrupts in order to identify the called subscriber, the central processing equipment instead, using appropriate detectors of the tones, completes the dialing by its recognition of the tone combinations.
Alarm systems employing a radio frequency transmitter and a frequency compatible receiver that couples into a telephone system to remotely dial a number and deliver a message into the receiver of the telephone of the number dialed are well known in the art. However, in the past such systems have been designed for use with telephone systems employing a digital sequence of switch opening type dialing and not for use with or to take the maximum advantage of systems employing Touch Tone.RTM. dialing.
For example, in U.S. Pat. No. 3,207,850 there is disclosed an alarm system which includes a battery powered radio frequency transmitter and a radio frequency receiver which is coupled to the telephone lines through a phone line activator, a phone station selector and a message player. The phone line activator is either external to or internal to the telephone circuits. The phone station selector is a device that either initiates or simulates a digital switch type of dialing sequence. The message player is made up of a phonograph disc or tape which carries a message and some appropriate form of reproducer or player device to convey the message which is on the disc or tape.
In U.S. Pat. No. 3,843,841 there is disclosed a remotely actuated automatic telephone care system which includes a small device adapted to be worn or carried by a person. The device transmits a radio frequency signal to a base unit that automatically dials one or more predetermined telephone numbers and plays back a recorded message. The base unit, which is designed for use with a digital sequencing type of dialing system includes a two track tape of which the lower tape contains dialing information in the form of a series of 1000 Hz tones.
In U.S. Pat. No. 3,560,657 there is disclosed an automatic warning system which responds to a warning signal energized by an outside agency by closing a switch which permits a power supply to energize the motor on a tape deck. The tape deck generates a plurality of single frequency pulses which are rectified and used to energize an electronic switch that provides data to a coupling mechanism and dials a remote telephone. After the telephone is dialed, the tape deck broadcasts a voice signal and then a further series of single frequency pulses that resets the system and dials a second number or the same number. The switch is then opened and the system turned off.
Other known references which are pertinent in one way or another to this invention are U.S. Pat. No. 2,766,358; U.S. Pat. No. 3,683,114; U.S. Pat. No. 2,022,991; U.S. Pat. No. 2,522,615; and U.S. Pat. No. 2,899,645.